In a conventional device for brush-polishing, a polishing brush is connected to a motor on the bottom of it, wherein bristles having a capability for polishing are fixed. The tips of the bristles contact a workpiece and the center of the polishing brush is horizontally rotated so as to polish the workpiece by the brush (hereafter, just called “polish”) (for example, see the Japanese translation of PCT International Application No. 2001-508338). To improve the capability for polishing of such a device for brush-polishing, increasing the speed of the rotation of the motor is one possible way. However, a motor that has great power is large, so that the entire device for brush-polishing becomes big. Further, due to the increase of the speed of the rotation a problem may occur, such as vibrations or a noise.
A device for brush-polishing that is not big and has a high capability for polishing is disclosed in Japanese Patent Laid-open Publication No. 2004-142058. In that device a polishing brush is horizontally rotated, i.e., rotated about its central axis, and horizontally revolved, i.e., revolved as if in an orbit, because of the rotation of the motor that is connected to the polishing brush. That is, the device for brush-polishing utilizes a planetary motion. In such a device, both the rotation and the revolution are caused by one motor. Thus the motor is subject to a large load. Further, the ratio of the speed of the rotation to that of the revolution is fixed. Thus the ratio is not adjusted in relation to any changes of the properties of the workpieces or the purposes of polishing the workpieces.
The present invention provides a brush unit that polishes a surface of a workpiece to be processed by causing a polishing brush to move as in the planetary motion and that allows an easy adjustment of any condition necessary to polish the workpiece in relation to changes of the properties of the workpieces or the purposes of polishing the workpieces. The invention also provides a device and a method for brush-polishing that use the brush unit. It also provides a system for brush-polishing that polishes both sides of a workpiece.